This invention relates to a method and apparatus for forming, filling, and sealing plastic bags or containers with various materials, and more particularly to a method and apparatus for eliminating the wrinkles that would otherwise form at the heat sealed seams of the plastic films used to form the bags or containers.
In recent years, processing machinery has been developed for filling plastic bags, pouches, and containers with dry particulate products or with liquid products. Typically, this machinery is referred to as vertical form, fill, and seal machinery because of the manner in which the bags are formed and then filled with product. Generally with such machines, a flat continuous roll of bagging material may be formed into a tube, sealed at the bottom, filled with product, and then sealed at the top. Examples of such machines and methods are numerous and include U.S. Pat. Nos. 3,826,061; 3,849,965; 4,077,308; and 4,090,344.
In typical vertical form, fill, and seal machines, a flat sheet of packaging material is first formed into a tube by automatically shaping the sheet into a tube, bringing the edges of the sheet together, and longitudinally sealing those edges at that juncture. A pair of sealing jaws are provided in the machine which are transversely movable toward each other to engage the bagging material, after it is in the shape of a tube, to form a transverse seal providing the upper closure for a lower bag and a bottom closure for a succeeding bag. The product to be placed in the bag is measured and introduced into the upper succeeding bag. Then, the sealing jaws are released and the bagging material is advanced. The sealing jaws are reactivated and again engage the bagging material to form an upper seal on the just-filled bag, and the procedure is repeated again and again. After sealing, individual bags are separated by a suitable severing mechanism.
In some cases, the bags, pouches, or containers are reclosable. That is, the bags include along one edge thereof mating rib and groove profile elements. Such reclosable zippered bags have been adapted for use in vertical form, fill, and seal machinery. See, for example, U.S. Pat. Nos. 4,617,683; 4,355,494; and 3,815,317. In those patents, the flat bag stock is manipulated by appropriate handling apparatus to fold it, mate the corresponding rib and groove elements to form a tube, and then the tube is handled in a manner conventional in vertical form, fill, and seal machinery.
One of the problems which has occurred in the past with vertical form, fill, and seal machinery has been that wrinkles tend to form along the edge seal lines of the bags during the edge seal operation. This wrinkling problem is due in large part to the fact that the bag tube, once filled with product, assumes and maintains a tubular shape. When the jaws of the sealing mechanism close about the tube stock, the presence of product in the tube causes the tube to resist flattening. Because of the lack of control over the movement of the edges, and their resistance to assuming a flat configuration, it is likely that wrinkles will form as the sealing jaws close and form the seal.
Attempts have been made in the past to overcome this wrinkling problem in conventional tube stock. For example, Wenger, U.S. Pat. No. 4,235,064, shows a vertical form, fill, and seal machine which includes a centerfold rod which is spring loaded to bear against the center line of the tube during filling and sealing thereof. Kelly, U.S. Pat. No. 4,534,159, teaches a form, fill, and seal apparatus which includes two pairs of stretcher fingers at opposite sides of the tube stock to provide opposing forces in directions perpendicular to the movement of the sealing jaws to flatten the tube prior to sealing.
The wrinkling problem is, if anything, even more of a problem where the tube stock is of reclosable bag material. The presence of the mated rib and groove elements at one side of the tube after filling the tube with product contributes to the difficulties in getting the opposing tube surfaces into a flattened configuration for sealing. Accordingly, the need exists in this art for a method and apparatus for removing the wrinkles from zippered tube stock prior to sealing.